1. Field of the Invention
The present invention relates to a Fiber-To-The-Home (FTTH) network for convergence of broadcasting and communication.
2. Description of the Related Art
In the prior art, in order to provide for the efficient exchange of an Ethernet signal which is a communication signal, a passive optical network (hereinafter, referred to as a PON) structure. In such a network, there is generally one optical line terminal (hereinafter, referred to as an OLT) that is located at a telephone office. The OLT is subsequently connected to an N number of optical network terminals (hereinafter, referred to as ONTs) that have been installed at homes.
In this PON structure, the efficiency of the network increases so much that Ethernet switches in the N number of ONTs share an Ethernet signal from an Ethernet switch in one OLT through a power splitter. In this type of structure, since continuous digital broadcasting signals must be transmitted to all subscribers in a single direction, there has been used a certain method of overlaying optical signals for digital broadcasting onto an Ethernet communication network.
FIG. 1 shows a construction for the conventional FTTH network as described above. As shown, an OLT 100 and a plurality of ONTs 200-1 to 200-3 are connected to each other by a 1×N optical power splitter 111 so as to form the FTTH network.
In a conventional network structure such as shown in FIG. 1, in order to service digital broadcasting and an Ethernet signal such as an Internet signal/video on demand (VOD) signal simultaneously, the OLT 100 includes an Ethernet switch 106, an optical transmitter 107, an optical receiver 108, and a wavelength division multiplexer 109 and processes the Ethernet signal through these devices. The Ethernet switch 106 switches downstream Ethernet information to each ONT and upstream Ethernet information from each ONT. The optical transmitter 107 generates a downstream optical signal for transmitting the downstream Ethernet information to the ONT. The optical receiver 108 converts an upstream optical signal into an electrical signal so as to transmit the converted signal to the Ethernet switch 106 for further communication with the Intent, or a Video on Demand. The wavelength division multiplexer 109 wavelength division multiplexes the downstream optical signal to transmit the multiplexed signal and receives the upstream optical signal. Also, the OLT 100 includes a Sub Carrier Multiplexing (hereinafter, referred to as an SCM) section 103, an optical transmitter 104, an optical amplifier 105 for amplifying an optical signal, and an optical coupler 110 for coupling with an Ethernet signal. The SCM section 103 modulates several digital broadcast channels of a digital broadcasting unit 101, respectively, from an exterior by a quadrature amplitude modulation (QAM) method, and also multiplexes the modulated channels by an SCM method.
The optical transmitter 104 optically modulates the multiplexed broadcast signal.
Furthermore, the optical signal transmitted from the optical coupler 110 is classified into an N number of powers by the 1×N optical power splitter 111 and the classified signals are distributed to each ONT.
Then, the optical signal that is distributed to the ONT from the optical power splitter is classified into a broadcasting signal and an Ethernet signal via a wavelength division multiplexing demultiplexer 112 for wavelength division multiplexing, which divides signals by wavelength. Further, the broadcasting signal and the Ethernet signal are processed by respective optical receivers 113 and 114. Herein, the broadcasting signal is transmitted to a set-top box (hereinafter, referred to as an STB) 300 and is passed through an RF filter in the STB 300. Then, only a desired RF signal is selected and decoded as a high definition television (HDTV) signal to enter a digital TV 500.
Also, the Ethernet signal is transmitted to an Internet/PC 400 through an Ethernet switch 116 which is then provided to a user. An upstream Ethernet signal sent from the user travels through the Ethernet switch 116 and is converted to an optically modulated signal via an optical transmitter 115. The modulated signal is transmitted to the OLT 100 through the wavelength division multiplexing demultiplexer 112.
The PON structure used for overlaying the conventional digital broadcasting and providing network service as described above has the following problems.
Firstly, the PON structure, in which one OLT transmits a signal to the N number of ONTs by means of the power splitting method, has a limitation in the number of the ONTs that can be in communication with the one OLT. According the current technology, since 64 divisions at maximum can be performed in consideration of a power margin, a digital broadcasting signal can be transmitted to 64 ONTs at a maximum by means of one analog optical transmitter.
Accordingly, when the number of the ONTs exceeds 64, since another PON system is additionally required as the maximum of the first PON has been exceeded, then the overlay operation must be performed by means of another analog optical transmitter, increasing the costs of the entire system.
Further, when 64 divisions at maximum are performed, an expensive optical amplifier, such as an EDFA, must be used next to the optical transmitter in order to increase the intensity of an optical signal and secure a carrier to noise ratio (CNR) for maintaining broadcasting quality. Furthermore, even in a case of a network utilizing an optical transmitter and the optical receiver, an expensive optical transceiver having a good property is required, increasing these costs of the entire system increases.
Furthermore, in a case of the conventional overlay method, since the STB receives all broadcastings, the STB of each subscriber requires a subscriber authentication and a real time accounting by a conditional access system (hereinafter, referred to as a CAS) system supporting encryption and decryption. Furthermore, since all broadcasting signals are transmitted to each ONT, an optical line having a large bandwidth must be used.